WESTERN NEW YORK HORTICULTURAL SOCIETY. 431 



RIPENING AND PRESERVATION OF FRUITS. 



BY DK. G. C. CALDWELL,, PROF. OP CHEMISTRY, CORNELL, UNIVERSITY. 



The decay of fruit is the final ending up of a series of chemical changes, the 

 beginning of which is away back at its first appearance after the flower withers and dies. 

 The green fruit behaves like a green leaf; it takes up carbonic acid from the air, and 

 water from either air or soil, and gives off oxygen, and makes what we call vegetable sub- 

 stance, such as cellulose of the walls of the multitude of very little cells or chambers 

 of which the fruit is built up, and which increase in number and size as the fruit grows 

 as we make a house larger by adding on more rooms, or adding to the size of those that 

 we already have. Then, in these cells, other vegetable substances are stored, such as 

 starch, fats, acids, pectin bodies, tannin, albuminoids and so on — perhaps not all of them 

 in the very youngest fruit, but all of them, sooner or later, and others besides. 



But, in the building up of the fruit, and stocking its multitude of cells, the fruit itself 

 is by no means required to do the whole of the work: it receives help from the other 

 green parts of the plant, whether a shrub or a tree, or a mere garden plant, like the 

 tomato. In the case of real fruits the most interesting stage of chemical change is 

 that of the ripening period, during which the fruit changes color, becomes softer, usuall> 

 sweeter and less astringent or puckering. The fruit loses its power more and more 

 as the departure from the original leaf green color widens, of making the material for 

 its own growth out of carbonic acid and water, and such matters as are drawn from 

 the soil; and instead of taking up carbonic acid and giving off oxygen, it comes more 

 and more to behave like animals in their respiration. It takes up oxygen and gives off 

 carbonic acid, and it comes to be entirely dependent on the green parts of the plant, 

 the leaves, for whatever more it may need of new building material, or of material to 

 put into its cells. This process of respiration in animal results, as you know, in a slow 

 burning up of certain substances in the body. Heat is a product of the operation, as 

 heat, more or less intense, is a product of all burning, whether slow or fast; if slow we 

 may see no fire, but there is heat nevertheless, and it is this heat that makes the living 

 animal body warm. So, if the ripening fruit takes up oxygen and gives off carbonic 

 acid, a slow burning must take place in it also; tannin is probably burned first, or is 

 among the first substances to be destroyed; the puckery character of the fruit grad- 

 ually lessens, and finally disappears altogether, as one of the important phases of the 

 ripening. This is true at least of the grape, and in all probability of fruits in general. 



Insoluble pectose substances change to soluble and the fruit become softer espe- 

 cially toward the end of the ripening process. The proportion of albuminoids increases 

 and consequently the fruit becomes more nutritious. The most important changes that 

 take place, however, are in respect to the sugar and the acids. These changes have been 

 studied more than any others; for upon the relative proportions of these two constitu- 

 ents, as well as on those subtle substances that give aroma and flavor, the eating quali- 

 ties of the fruit depend altogether. The proportion of sugar increases from the 

 beginning — sometimes steadily, as in the peach and strawberry. In the gooseberry and 

 cherry a sudden increase has been observed at just about the time when there is a cor- 

 respondingly rapid growth in the size of the berry. In the grape the sugar increases 

 rapidly also through a certain period, which some investigators make out to be longer 

 than others, and some make later in the season than others do. 



The proportion of acid also usually increases through at least a large part of the 

 period of ripening; but in the case of some fruits it afterward falls off, and in some 

 cases, as in the strawberry, it may rise again. In the grape the acid seems to diminish 

 steadily, and it has been supposed that it was converted into sugar — a change which, 

 though not possible in our chemical laboratories, may be brought about in the plant's 

 laboratory. But it is not probable that this is the source of the sugar. It has been 

 fairly proved that sugar is transported into the fruit in the current of sap from the 

 leaves; and it is generally believed that when the acid increases too, it also is carried 

 into the fruit from without. 



While, in the grape, the greater sweetness of tlie ripfe fruit, as compared with that 

 whiA is only partially ripe, may be due to the lessened proportion of acid, as well as 

 the increased proportion of sugar, it is evident that this can not be the case in those^ 

 fruits whose acid increases as the ripening progresses. The ripe fruit is sweeter only 

 because the sugar increases more rapidly than the acid does. 



As fruits differ in their method of ripening before being plucked, so do they differ, and 

 much more, in their methods of after-ripening, when detached from the plants on which 

 they grew. All fruits undergo a certain amount of ripening on the tree or vine; but 



